Hmm. Since I apparently missed the original poster's reply, I shall answer this belatedly.
If you are very energetic and excited about going to grad school, then perhaps it is right for you to go straight on. Many people I know, though, including myself, are a little wiped out after undergrad. I wish that I had taken time off after undergrad because I started grad school exhausted from the push at the end of undergrad. Even with the summer off, it wasn't enough time for me to relax. That made the first year of grad school all the harder. Had I taken enough time off for me to recharge my batteries, then I would have had a better time with everything. That being said, you need to be careful that you don't get sucked into the void of never returning to finish a degree.
As for the question of why after 10 years you couldn't return, it's true, you could, but the university may look a little harder at the application since there are usually great advances in your field in the meantime.
And, dfx-, here's the breakdown of how things go here in the US:
High School (4 years)
Undergrad (College/University, 4 years, leave with a BA/BS, bachelor's degree)
Grad school (University, MA/MS/Masters, also DA/PhD/Doctorate; years vary by degree type, but typically 2 years for masters, 3 for PhD in chemistry, though they are typically combined now)
A university offers graduate studies; a college by definition does not. However, you can also get a bachelor's from a university.